1. Field of the Invention
The present invention generally relates to a method for displaying images in a raster display controlled by a computer. In particular, the present invention relates to an anisotropic filter mechanism required for reconstructing, or scaling, discrete, stored images or for subjecting same to a perspective projection for the purposes of representation on raster display elements of a high quality. The above-mentioned discrete, stored images will be referred to as textures below. In particular, the present invention relates to a method for analyzing and modifying a footprint depending on a specified number of texture elements touched by the footprint in a graphics system providing the texture elements having a resolution.
2. Description of Prior Art
A “footprint” is a perspective projection of a picture element (pixel) of an object onto a curved surface. A “footprint” may be a convex quadrilateral representation reproducing the approximated result of the perspective projection onto a regular texel grid (texture-element grid) of a square picture element (pixel) of an object onto a curved surface.
In associating textures with picture elements (pixels) of an object, known graphics systems, e.g. OpenGL graphics systems, operate in such a manner that a footprint of a pixel of an object has one or more texture elements having a desired resolution associated with it, the footprint being approximated by a square. The disadvantage is that the approximation here is always effected by a square which is either too large or too small and that the shape of the footprint is not taken into account.
The resolution desired results in a texel size in a texel grid underlying the footprint. Various mipmap level exist for predetermined texel sizes. If a resolution is chosen which leads to a texel size for which there is no mipmap with a suitable resolution (level), the texture must be calculated at high expenditure.